1. Technical Field
The present invention relates to a positive photosensitive resin composition, a method for forming a cured film, a cured film, an organic EL display device including the cured film and a liquid crystal display device including the cured film.
2. Related Art
Organic EL display devices, liquid crystal display devices and the like include a patterned interlayer dielectric film. In order to form an interlayer dielectric film, a photosensitive resin composition is widely used from the viewpoint of reducing the number of processes for obtaining an intended pattern shape and achieving sufficient flatness.
In addition to physical properties such as favorable insulation properties, solvent resistance, thermal resistance, hardness and suitability for indium tin oxide (ITO) sputtering, there is a demand for an interlayer dielectric film used in the display devices as mentioned above to exhibit high transparency. Thus, use of an acrylic resin, which is highly transparent, as a component for forming a film has been attempted.
Further, with regard to a light source for exposing a photosensitive resin composition to light, as a direct drawing method by exposure to 355 nm laser light, use of various light sources in pattern formation, such as g and h line-mixed light sources from which i line is excluded, in addition to conventionally used g, h and i line-mixed light sources, has been attempted.
As a photosensitive resin composition suitably used for forming interlayer dielectric films, Japanese Patent Application Laid-Open (JP-A) No. 5-165214 proposes a photosensitive resin composition including: (A) a resin that is soluble in an alkali aqueous solution and is a copolymer of (a) an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride, (b) a radical polymerizable compound having an epoxy group and (c) another radical polymerizable compound; and (B) a radiation-sensitive acid-generating compound.
Japanese Patent No. 4207604 proposes a radiation-sensitive resin composition including: (A) a high molecular weight polymer having an acetal structure and/or a ketal structure and an epoxy structure, and having a weight average molecular weight of 2000 or more (polystyrene converted) measured by gel permeation chromatography; and (B) a compound that generates an acid having a pKa of 4.0 or less when exposed to radiation.
JP-A No. 2009-98616 discloses a positive photosensitive resin composition that includes at least: (A) a resin that contains a structural unit having an acid dissociative group represented by the following formula (1) and a structural unit having a functional group capable of forming a covalent bond by reacting with a carboxyl group, the resin being insoluble or hardly soluble with respect to alkali but becoming alkali-soluble upon dissociation of the acid dissociative group; and (B) a compound that generates an acid when exposed to actinic light or radiation. In the following formula (1), R1 represents a hydrogen atom, a methyl group, a halogen atom or a cyano group; R2 and R3 each represent a hydrogen atom or an alkyl group but at least one of R2 and R3 is an alkyl group; R4 represents an alkyl group or an aralkyl group; and R2 and R4 or R3 and R4 may be bonded to each other to form a cyclic ether.

On the other hand, a microlens having a lens diameter of approximately 3 to 100 μm or a microlens array, in which plural microlenses are arranged in a regular manner, is used as a material for an image formation optical system of an on-chip color filter used in facsimile machines, electronic copiers, solid-state image pickup elements and the like, or as a material for an optical system of optical fiber connectors.
With regard to a method for forming a microlens or a microlens array, for example, a method in which a resist pattern corresponding to a lens is formed and then heated to allow the pattern to melt-flow, and the resultant is used as a lens as it is, and a method in which the shape of a lens is transcribed onto a base by dry etching using a mask formed from a melt-flown lens pattern, are known. In the formation of a lens pattern, a radiation-sensitive resin composition is widely used (for example, see JP-A No. 6-18702 and JP-A No. 6-136239).
The element on which the above-mentioned microlens or the microlens array is formed is then subjected to a process for removing a dielectric film of various kinds formed on a bonding pad, i.e., a portion on which a wiring pattern is formed. Specifically, a planarization film or a resist film for etching is formed on the dielectric film, and exposed to light via a desired mask and developed to remove an etching resist at a bonding pad portion. Subsequently, the planarization film or the dielectric film is removed by etching to expose the bonding pad portion. Therefore, the microlens or the microlens array needs to be solvent resistant and thermally resistant during a process of forming a planarization film or an etching resist film or a process of performing etching.
In view of the above, it is necessary that a radiation-sensitive resin composition used to form a microlens such as the above have a high sensitivity and a favorable preservation stability, and that a microlens formed from the composition have a desired radius of curvature, high thermal resistance, high transmittance and the like.
In addition, an interlayer dielectric film or a microlens thus formed tends to cause exfoliation of a pattern from a support due to a developer infiltrating therebetween when the type of the exposure light source or the amount of exposure is changed from an optimal value. Therefore, there is a need to strictly regulate the exposure amount or the like, and such a need causes a problem in terms of product yield.
As described above, a radiation-sensitive resin composition used to form an interlayer dielectric film or a microlens needs to be capable of forming a pattern at high sensitivity upon radiation exposure, and exhibit favorable preservation stability. Furthermore, when a photosensitive resin composition is used to form an interlayer dielectric film, it is desired that the composition be less dependent on the type of exposure light source or the exposure amount, and the obtained interlayer dielectric film exhibits high thermal resistance, high solvent resistance, low dielectric constant, high transmittance, and the like. On the other hand, there is demand for a radiation-sensitive resin composition used to form a microlens to form a favorable melt shape (an intended radius of curvature) as a microlens, high thermal resistance, high solvent resistance, and high transmittance. However, a radiation-sensitive resin composition that satisfy all of the requirements as mentioned above has yet to be known.
The present invention has been accomplished in view of the above circumstances, and an object of the invention is to provide a photosensitive resin composition having a high exposure sensitivity, being capable of forming a pattern having a favorable shape even when the exposure conditions are changed, and being capable of forming a cured film that exhibits excellent strength, excellent thermal resistance and high transparency.
Another object of the invention is to provide a cured film that is obtained from the photosensitive resin composition of the invention and is suitable for an interlayer dielectric film, a method for forming the cured film, an organic EL display device having the cured film obtained by the method, and a liquid crystal display device having the cured film obtained by the method.